Since neutrons have no charge and do not interact significantly with most materials, neutron converters are needed to react with neutrons to produce charged particles that can be easily detected by semiconductor devices to generate electrical signals.
Conventional 3He proportional tubes are simple neutron detectors that may achieve high thermal neutron detection efficiency. For example, a 2-inch diameter tube filled with 10 atm of 3He gas may reach 80% detection efficiency, although the detector normally operates at lower pressure settings thereby reducing the efficiency. Furthermore, the use of these proportional counter type devices is somewhat encumbered by the required high voltage operation (1000 V), sensitivity to microphonics, and high pressure; resulting in significant complications in routine deployment and air transport.
Solid state thermal neutron detection techniques generally utilize a planar semiconductor detector over which a neutron reactive film has been deposited. Upon a surface of the semiconductor detector is attached a coating that responds to ionizing radiation reaction products upon the interaction with a neutron. The ionizing radiation reaction products can then enter into the semiconductor material of the detector thereby creating a charge cloud of electrons and “holes,” which can be sensed to indicate the occurrence of a neutron interaction within the neutron sensitive film. The charges are swept through such configured detectors via methods known by those of ordinary skill in the art and registered as an electrical signal.
Another geometry includes etched trenches, slots, or holes in semiconductor materials having dimensions on the micron scale or larger that are filled with predetermined converter materials and configured with electrodes so as to produce detectors similar to the planar detector geometries discussed above.
Conventional solid state radiation detectors, however, suffer from efficiency, flexibility and scalability issues.